What role does tTG IgA play in Haut?

tTG IgA (antibodies against tissue transglutaminase) is a well-established serological marker for celiac disease. In the skin, its role is indirect: in dermatitis herpetiformis (DH), the cutaneous manifestation of celiac disease, IgA antibodies deposit in the papillary dermis. These antibodies primarily target epidermal transglutaminase (eTG), which is structurally similar to tTG. Cross-reactivity of tTG IgA with eTG leads to immune complex deposition and neutrophil infiltration, causing itchy vesicles and papules. A positive tTG IgA blood test supports the diagnosis of DH, even though the skin lesions themselves are mediated by eTG antibodies. Evidence is human-strong, based on clinical studies and guidelines. Caveat: tTG IgA alone is not specific for skin manifestations; direct immunofluorescence of skin biopsy (showing granular IgA deposits) remains the gold standard.